In our previous issue, we discuss about properties of lubricating oil and what to look for when buying or replacing them. Ezine Article
Today, we want to find out as to when to replace lubricating oil. If you have a large quantity of lubricating oil to change, it is going to burn a hole in your pocket. So most plant operators try to preserve properties of lubricating oil for as long as possible.
One of most important functions of lubricating oil is to reduce friction between moving parts of machinery. But there are other features to look at.
When do you know that oil needs to be changed? Below is a rough guide: 1. Viscosity has changed by 10% 2. Flash Point has dropped to 150 degree Celsius 3. Water Content has reached 2% 4. TBN, or Total Base Number has reduced by 20% 5. Insoluble Content has increased to 5% of oil
Due to oxidation of oil when exposed to heat and oxygen, viscosity of oil tend to reduce. With reduction of viscosity, film of oil between rubbing metal surfaces becomes more difficult to maintain. This results in metal to metal contact, micro seizures that leads to scuffing, abrasion and other damages.
In large diesel engines, fuel oil from dripping injectors or fuel pumps sometimes finds their way into lubrication oil sump. This has tendency to reduce flash point of lubricating oil. In addition to reducing viscosity that is detrimental to lubrication, this contamination with fuel oil can be quite dangerous. If there is a hotspot in any of rubbing parts, this can lead to a crankcase explosion.
Water can also find its way into lubricating oil from leaks in cooling water system o-rings or gaskets. In addition to reducing lubricating properties of oil, presence of water in oil can give rise to bacteria or fungal growth, which will quickly damage oil properties as well as contributing to acid corrosion and oxidation of oil, changing chemical composition of oil itself. However, if water content is below 0.5%, it can still be removed by centrifugal purifiers.